Frontier Airlines EarlyReturns - Do upper bins fill up quickly?

I'd appreciate some input/advice about the likelihood of upper bin space being available for a couple upcoming flights, SMF-DEN-DCA and return. I haven't flown Frontier before and have been told that it's probably easier to find room for my business-size roller (17" x 15") if we sit near the back of the plane. On the last 2 flights we took on UA, the GA announced that all rollers had to be checked at the gate and would not be allowed on the plane, due to lack of space. This would not work for us since the bag will contain our laptop and other valuables we don't want to be separated from. Carrying a separate laptop bag wouldn't work in our case either.

I realize every flight is different, but if there are some common trends, my questions are:

1) Is it very common for passengers to be required to check carry-ons that won't fit under the seats?

2) Will sitting near the back of the plane make it a lot easier to find upper bin space for 1 roller?

Thanks in advance for any help.

2) Will sitting near the back of the plane make it a lot easier to find upper bin space for 1 roller?

Thanks in advance for any help.

Sitting near the back will put you in Zone Three. Zones one and two board first and fill the bins moving backward.

Zone One will guarantee you bin space. That is Rows One to Four. STRETCH.

And boarding earlier will always give you the option of placing your bag farther back if all the bins above you are taken.