This would be the best solution, however for most of us, mortals, unreachable with serious, difficult attack (it means also correct distans, not zombi attacking from 10 feet away).
Timespace is so very small, that human brain can't handle it normally.
Uhmmm.... that is why you practise so you do not need to think. Your visual system has been (or should be) trained to properly 'read' the distance. Kimusubi, ma ai, kino nagare all principles need to come together in that exact moment. I always interpret Aikido as to be able to do the right thing at the right time.
When your partner regains balance during a technique something went wrong in your execution (duh). Most of the time you are not 'leading' your partner sufficiently and thus your partner stops.
When you practise chudan tsuki, alternately practise with and without tanto. Distance changes only few centimeters, but you must be able to 'see' this and move accordingly. Practise such that each time there is only but an inch space between fist/tanto and you, with different partners.
Another exercise: have partner attack with bokken (shomen) and slightly move of the center/attack line and enter and put your hand on his/hers.
many, many, many more exist....