Baffle wall and bass trapping

I am going to build a dedicated room in the next months and am thinking of doing a baffle wall. My speakers are 18" deep so the baffle wall would be about 20" from the wall. I would like to reduce the reverb time in the low frequencies by filling the area behind the baffle wall with fiberglass, but would this actually make a difference when the baffle wall is made of 1.5" thick MDF? Having 20" deep fiberglass directly in the room would definately improve the reverb time, but what is the effect when the MDF is placed in front of it? I would like to fix the potential SBIR and improve imaging by using a baffle wall, but if this means an increased reverbation time in the lower frequencies compared to alternative solutions without a baffle wall, I dont know what would be the best thing to do.

Would appreciate all inputs.

Thanks for your answer.

I could just place the speakers/subs and fill the empty areas with 20" insulation without making the MDF baffle wall (sort of a solid insulation baffle-wall with cut outs to speakers/subs). I would not get the increase in sensitivity I would with the baffle wall, but my speakers are 97db, 1w anyway. I just dont know if the insulation would get rid of the unwanted reflections from the back wall. But 20" is a large amount, so it would definately improve it compared to free standing speakers.

Are there any drawbacks in the solution above?

I found my old physics book and if I remember correctly, my dip/peak pattern if my speakers are 20" from the wall behind them, will be something like this:

Freq, Type
172hz Dip
344hz Peak
516hz Dip
688hz Peak
860hz Dip
etc...

This means, that the back wall must be able to absorb 172hz to completely get rid of the artifacts. By using this page as reference (http://www.bobgolds.com/AbsorptionCoefficients.htm), this should be easily doable.

Again, all inputs are appreciated - I cant be the first one to have this dilemma when designing the room?