Some rambling from a new NSCA Master class shooter.
I practice with Full and Full then open up to Mod and Mod for registered targets. I almost never change a choke during a shoot.
He’ll break more targets in the short term with open chokes, he’ll break more in the long term by using tighter chokes and learning to shoot those targets better.
I watch shooters struggle to hit 80 with the same Skeet/Skeet or IC/IC that they’ve been shooting for years. IMO you have to keep pushing your comfort zone, if you like IC shoot Mods, if you feel comfortable with Mods shoot I Mods. Get to where you can comfortably shoot Fulls at any target.
Yes I miss targets with my Full chokes, the difference is I usually know where and probably why.
He’ll hit more targets the more targets he hits.

He has to build the bird bank/data base/subconscious. It takes time. Only hits add to the bird bank, misses don’t teach you anything. When you miss a target you need to make a change, fix it, DO NOT do the same thing again and expect a different result.
In addition to experience, clay targets are are also a confidence game. Tighter chokes + more experience = harder breaks = more confidence = more breaks = you get it. It takes time though, you can’t just screw in Full chokes and instantly be inkballing targets.
IMHO, YMMV, no refunds, no targets were harmed in the making of this post.