In cutting down techniques like ikkajo, sankajo, yonkajo... Don't try to hook your wrist over uke's arm and push them down. If you do this, your thumb will end up on the inside making it impossible to properly grab the arm.
After the front strike, don't grab uke's wrist too early. If you do
this, as you cut down and rotate your partner's shoulder, your hand will
end up under your partners arm and therefore lose the stability and strength in
Your upper hand wrist should be turned slightly back like in hiriki no yosei to keep the stability in your arm and also prepare your thumb and index finger for the final grab.
Hint: you should almost always see wrinkles in your wrist.