It's just the sensibility you have regarding sexual depictions. If you immerse yourself in it maybe you'll feel it too, instead of thinking about it from a 3rd person perspective. The same is possible with books (text), the ability to imagine the situation and really get into it. Here (webtoons) the process is even simpler than with books, because these are pretty graphic depictions so the process of imagining is simplified. Apart from that, I don't know if that was your intention or not, but saying it's funny seems like you're making fun of me...
Ohh ok, my bad then! Yeah, there's lots of perspectives and perceptions, everyone is different. Personally, I always had that imaginative streak and it's something that developed through the years, with stories in general not just yaoi. I started noticing it with books, when I would start feeling like the characters I read about. Regarding yaoi, I don't read it to get horny or something, but sometimes it happens.
My god... That panel with an above perspective of Ian is just marvelous, I mean the sex appeal and pose it's just too much.
P.S. It made me horny, I imagine TJ (⊙o⊙ )