I think sensitivity to arousal is psychological and physiological (like yeah, what else is there?) .
You already stated what thoughts get you excited, so it is partly just a matter of engaging the necessary thought patterns.
So think Big Dick thoughts. It helps me get hard when I am pumping.
When I was an adolescent I could hardly stop having erections, anytime and anywhere. In college I was reluctant to engage in slow dancing at the clubs because I would always get a stiffy.
Just being in the presence of an attractive girl would sprout a trouser tent.
Now in my 50’s it takes some mental and physical effort to get it up, though I would not consider myself suffering from ED. I can still get nocturnal and morning erections.
Even in my late 30’s I could control my arousal even in the presence of a hot woman teasing me for sex, or a naked stripper giving me a lap dance.
So part of it is your willingness to be affected by stimuli and thoughts, and part is just your overall sensitivity to stimuli.
I think it is also dependent on your physical condition. I find that I get bigger erections after a short rest period from doing PE, maybe a day or 2. Or if I have been doing mild pumping for a couple days, and still plump, I can sprout a pretty girthy erection if I am not fatigued from over training.
Just pay close attention to your activity and thought patterns.