Why were there no religious wars in Poland?

It would seem that religious toleration in Poland became a necessity because borders with Lutheran Prussia and Orthodox Russia kept changing and people had to be reabsorbed into Poland. Also people fled intolerance in Prussia and Russia going to Poland for sanctuary. Poland needed France and Austria as allies against Prussia; therefore, it was wise to remain officially Roman Catholic while allowing Protestant and Eastern Orthodox to worship freely.

The Polish political system had its roots in medieval society : the king was elected by nobles (like a tribal chief). Once nobles chose to change their religion there wasn't any absolutist monarch that could stop them. Besides people wore religion more lightly than is realised (of course history records the fanatics but most people were socially religious). It was fanatical Jesuits who forced out other faiths and changed Poland from pluralism to exclusively Catholic.

Your question identifies, and hypothesizes a correlation between distance from Rome and pro (or anti) Catholic leanings. Under this hypothesis, Poland ought to be a "conflicted" country because of its "middle" distance.

In seeking a correlation (that may be false), the hypothesis overlooks causal variables that affected other "middle distance" countries like England and Bohemia, and not Poland.

In England, for instance, the anti-Catholic spark came not from religion per se, or relations between countries, but rather King Henry VIII's desire to divorce Catherine of Aragon, and marry Anne Boleyn. The Pope, who was practically a hostage of Catherine's nephew, Charles V, couuld not allow this. That's why Henry VIII broke with the Catholic church and set up the Church of England.http://www.greatsite.com/timeline-english-bible-history/king-henry.html

In Bohemia, anti-Catholic feeling went back to the early 15th century, to the Hussite rebellions, which were aimed against Austrian overrule. This pre-dated Martin Luther and "mainstream" Protestantism by almost a century. http://en.wikipedia.org/wiki/Hussite_Wars

In Poland, on the other hand, there were no anti-Catholic irritations. In fact, Poland had a history of religious tolerance going back to the 12th century, when King Boleslaus III welcomed both Jews from western Europe and Islamic Tartars from the east. http://en.wikipedia.org/wiki/Hussite_Wars Thus, when it was offered the alternative of Protestantism, Poland could accomodate both (plus Russian orthodoxy and others).

In fact, Poland had at least one internal religious war, namely, the Khmelnytsky Uprising in 1648–1657, right at the end of the 30 year war in Central Europe.

Religion, ethnicity, and economics factored into this discontent. While the Polish–Lithuanian Commonwealth remained a union of nations, a sizable population of Orthodox Ruthenians were ignored. Oppressed by the Polish magnates, they took their wrath out on Poles, as well as the Jews, who often managed the estates of Polish nobles. The advent of the Counter-Reformation worsened relations between the Orthodox and Catholic Churches. Many Orthodox Ukrainians considered the Union of Brest as a threat to their Orthodox faith.

You can read more in the linked wikipedia article as well as this one.

Poland was indeed involved in the 30 Years War, sending death squads to aid Habsburg allies in Bohemia and getting decked when Bohemia sicced the Ottoman Empire on them.

At this time, Poland-Lithuania was far more unified politically under the Magnates and royalty than the Holy Roman Empire... and nobody kid themselves, the 30 Years War was a political as well as a religious war. Rising European powers sought to solidify their power into what we know now as a nation-state, and the implosion of the Holy Roman Empire gave them the opportunity they needed. Distance from Rome was not as much of a factor as the political landscape - Ireland remained Catholic, mostly to spite their regional rival, England, and they were a very long way from Rome - and many Swiss cantons became protestant, despite bordering on what's now Italy.

The strong leadership in Poland-Lithuania allowed it to quell internal cultural strife with the Warsaw Confederation, which granted religious freedom to the subjects of the Commonwealth. This was something of a tradition for the area, going back to the Statute of Kalisz, which formalized tolerance for Jewish subjects, and the continuation of the toleration policies of Zygmunt II.

This dual policy - tolerating protestants at home and slaughtering them abroad - kept the peace without endangering Catholic rule.