It does make a difference, people can just be forgetful and not think about it. Mostly if their just running through a playlist of different videos. Just try not to seem rude about it, and don't push it too much.
Commitment consistency bias is best way I think to ask for subscribers. Create a enjoyable experience (the content), affirm the experience at the end of the video, (ex: did you enjoy watching this review?), in their head they should say yes, now you have them already commited through a simple question, then follow it up with with (ex: well, im glad you enjoyed! make sure to subscribe so I can continue to provide you more great reviews such as this one for your enjoyment). Theres definitely several other ways.
ex: its like a marketer saying, "yo you want to make more money?" and clearly you would say yes. Then the marketer would say "well heres a program for you to make more money." u dont want to do the program but in your head you already kind of made a commitment to wanting to make more money to this marketer. so it makes it hard to decline. "well didn't you say you wanted to make more money? -marketer
If you say it a end of a video, it shouldn't interfere at all with any of the content so I don't see the issue. You can really do it whenever you could even make little small pop-ups reminding people to subscribe. theres endless ways.