delagina, that's precisely what has refrained me for giving advice, since I am not expert nor trained so I have been looking some resources to see if something could be learnt short term, and if the "free field" pressure results lower than the inciding pressure, the front pressure is shown in the numerical examples in the text be higher than the inciding pressure, as you have also met; this a device of air confinement or whatever, but since not expert I have preferred to refer you to it.
What precisely I haven't understood from the text is that first goes for what in the uploaded page, then goes for a separate case for the front of a building (then sides, rear, roof as well) to find the bigger load you are finding. Now, in my mind that kind of thing seems mainly reasonable if the extent of the obstruction is as big as to produce confinement, other than that, it would make scarce sense to get some evaluation like that in the uploaded page, that would correspond to minor obstructions to the blast unable to show the confinement effects bigger surfaces are able to develop. But whilst I clear the matter better wait for expert advice.
