Save your money and get the smaller backing plate for the Flex, which allows you to use 4" conventional pads and the 5" Lake Country Hybrid pads (which has a 4" velcro side and 5" foam side).
Plate
FLEX XC3401 Changeable Backing Plate System
Hybrid pads in 5" (recommend orange, white, black) - risk some blue if you are adventurous.
Lake Country Hybrid Power Finish 5 Inch Foam Pads
Here's how I order them, generally in bulk.
I had a Meg's DA (G220v2) in the past, after getting the Flex with 4" plate and 5" hybrids I forgot about using the G220v2 DA for a while.
Then, I got the G220v2 again to see if it would ease things with smaller pads, used it for a panel and sold it right away - too much vibration, noise, and much less power compared to the Flex.
Nothing against PC style machines - I still like them, but if I had both a Flex with 4" plate and a PC with 3-4" plate, I can't cite a situation where I'd grab the PC for the same job.
Generally smaller spots are also intricate areas: this will give your 'underpowered' DA less rotation and more bog down than polishing action - you don't want that happening.
Here are some pics of the Flex with smaller plate for you to take a look. Rarely you'll find a place where the 5" hybrid won't fit. If you find it, 4" pads will do it fine.
The first Flex is fitted with 4" plate, the second with standard 5.5" plate, and the third is a Rupes 21 with standard 6" plate.
Here Flex is fitted with 4" plate and 5" hybrid orange cutting pad
In action (not the best example of smaller spot / intricate area, but...)!:
5" hybrid white polishing pad
Ready for action:
On the following pic, I'm using LC Microfiber pad (4.25") on the 4" Flex Backing Plate
The Rupes with MF for first cut, followed by Flex + 4" plate and Hybrid pad for secondary cut / refinement (I always follow a MicroFiber pad with a foam pad). The 5" pad and Flex Forced Rotation guarantees an even cut / finish in virtually ANY panel design.
On this scenario, I've used the Flex with 4" plate and 5" hybrid for cut (precision), followed by a fast refinement with the Rupes 21 and a large 6.5" flat finishing pad (speed):
4" flat finishing pad where 5"+ seems too large
In the end, I sure maintain all my respect for PC-style machines and it's users, but the way I'm working lately follow: 6.5" Hybrid Cutting pad on the standard backing plate / 5" Hybrid Cutting pad on the 4" plate - whetter they fit.
Please, the above text / images are just for illustration of my point of view, not the only or right or best way to work. Hope that adds some ideas to help you solving your question.
Kind Regards.