Boy, Oh Boy! Towshend!

The difference is cosmetic/aesthetic so get whichever one you think will look the best. To my eyes as long as the Podium is at least as wide as the speaker then they have a balanced appearance. If you go up in size to the next bigger one it gets you nothing in performance just a different look. Because drivers are mostly on the front baffle this puts the center of gravity just a little bit forward. What this means is if you get a bigger Podium you will have a bit of room to put the speaker a bit farther back on the Podium. But again this is all for how it looks. They are so easily adjustable you will be able to easily balance perfectly either way. 

Anything like this I always call John Hannant at Townshend, he has always had great suggestions and has yet to steer me wrong. 

Ok thanks all. Yes I liaised with John. It seems both would work and I was wondering if practically speaking it was better to have bigger ( or “exact fit”) based on real-life experience.
Also my floor is tiles. Would it still be possible to move a bit the speakers if needed with the podium in place?

My Podiums arrived and I installed them last night.
Interestingly one of the first things I noticed was the greater depth perspective and placement of performers/instruments in depth and in relation to each other. 
Probably the most important improvement is in tonal discrimination and clarifying of small details - you start to notice all manner of things in familiar music. 
These are preliminary impressions so far but hard to hear this as anything but an emphatic improvement.
I posted some pictures in another thread elsewhere if any ATC owner is interested how they look - I'll add these to my Audiogon system in due course. 

Your speakers fit perfect!!  The details as you mentioned. I have numerous hi Rez album rips that I thought where pretty quiet. Now surface noise and the pops and clicks are much more defined. Got to take the good with the bad. Check out Pat Metheny new album  Side-Eye NYC.  It’s live with some of the best percussion I have heard.  

moby2004- Yes you can adjust speaker position of the Podiums with the speakers on them. Just keep in mind each corner being on springs moves not only up and down but side to side. So after moving them be sure to check each corner to make sure they all still have clearance in every direction. I like to go corner to corner, give it a little nudge, and if it binds or rubs then adjust by pushing the base of the pod. Not the Podium, just the very bottom part. Being on tile you lucked out this is much easier than carpet.  

Tobes- That is by the way a good description of the sound. I have now heard these under 3 sets of speakers, all with similarly excellent results. The improvement with Brandon's Pendragon XL was like a whole system/room overhaul! When you talk about noticing new things in familiar music, for sure. It has been a while since I went through that with mine. When we set Brandon's up I heard the improvement but he is of course far more familiar with his room and music and was leaning forward mouth literally open gushing and finding it hard to believe how much more he was hearing. I was watching laughing, remembering what it was like for me. It really is hard to believe something like this can make so much difference.