Re: Larger/stronger opponent
I don't see why it matters if the uke is junior. i don't think the OP said that. It's interesting and symptomatic that uke is being blamed for nage's technique not working. There's a good chance uke is feeling muscled and just not responding to being pushed around. The OP might want to ask. Atemi goes both ways. If nage feels free to toss in the odd atemi so should uke. Same for judo and other extra stuff.
It sounds like this was static practice. Some folks can make static techniques work without forcing things. Most people (me especially included) can't, in my experience. Resorting to tricks is more about winning than about practicing. When my nages do that I give up and fall. They are signaling they don't want to practice anymore and I don't care if I lose when I'm not competing.