Reading these aloud, I don't notice a distinction in pronunciation, but it seems like there should be.
Question: What's the difference in pronunciation between kuàir and kuàr?
Reading these aloud, I don't notice a distinction in pronunciation, but it seems like there should be.
Question: What's the difference in pronunciation between kuàir and kuàr?
They have the same pronunciation.
The wiki page on Erhua lists the IPA of both finals ("uar" and "uair") to be [wɐʵ]
When you pronounce the two terms with an 儿, they sound the same.
The difference in pinyin is due to the original word without 儿.
块:kuài 跨:kuà