Is it ok to use more than half a capful of Rogaine to cover all top of the head?

It's very mportant to follow the instructions. The dose is 1/2 capful twice daily for men. Side effects of dizziness, heart palpitations, heart rate problems can occur if those proper dosing is not respected. It's rare - but certainly can occur. Patients using too much minoxidil don't feel well and can get sick, even end up requiring medical attention. Please respect the dose. For patients who feel there is just not enough medicine to spread around I often recommend the 5 % solution instead of the foam. You can use up to 1 mL (25 drops!) twice daily. That might be easier to apply 

Using the liquid is a good idea and measuring how much you use is also good.  I generally recommend that the nightly use should be done after a hot shower when the pores and circulation of the scalp it highest.  Once a day application is fine