PMC IB1's close to rear wall, is this O.K.?

I don't have either of these speakers.

However, assuming that by "Proac rear porting issues" you mean too much bass boost between 80 and 100 Hz then this will be an improvement; the IB1 is much flatter in the overall bass than the Proacs, which should be a significant advantage when placed near walls or corners (where you get up to +6 db bass boost anyway).

Thanks Shadorne for your answers. By rear porting isssues I do mean the bass boost problem as I've described in other threads. This isn't really a problem when the speakers are out into the room say 4-5' but I've tried them closer to the wall and it just gets too much. I am assuming that the rear port will load up when closer to the wall but maybe I'm wrong.
Am I correct that you are an ATC user? As I mentioned at the beginning of this post, I've been looking at some PMC's which I think are similar except for the transmission line vs a sealed enclosure. Do you have experience with other British monitors such as the Spendor 100's and Harbeths?

It is hard to say if you are going to have issues with placing IB1s close to the back wall.
I have IB2 and they are approximately 4 ft from the back wall, in a room that is approximately 18X18ft of unusual shape with no corners, so I have no issues of any kind with bass, ASC tube traps did almost nothing positive in my room (I had a chance to try).
A friend of mine has IB2s less than 2 ft from the back wall, in a room that is approximately 1/3 smaller than mine, of classical shape, but he managed to get quite good performance without huge peaks and dips by treating the room acoustically (pair of 13” tube traps, acoustic panels on side walls and ceiling).

If I recall bass goes like this Spendor - Harbeth - PMC - Proac in increasing order. ATC is actually regarded as bass lean by most people compared to "average" consumer speakers that tend to be a little bass heavy (bass sells).