1 1/2" is not way too skinny, tho they might like the 3 1/2" side up better.
..and it look to be long enough tho I can't see pic real good.
1 foot of roost length per bird works well, they sleep on less but need that 'extra' space to get settled during the nightly RoostTimeRumble.
You could add a lower roost too, to help them get up there, or a ramp, or just put them up there a few times and it might be just fine where it is.
Keep roost about a foot higher than nests so they don't start sleeping in nests.