Inasmuch as means because, and so more effective writers will seek to replace a more lengthy phrase (inasmuch as) with a single word that means the same thing (because). Conversely, many writers use insofar as in place of since, thinking they are also equivalent. But such is not the case.
Insofar as means to the extent that; thus, more effective writers will use insofar as when they wish to convey that exact meaning. If they want to convey the meaning of since, they will use since since (pun intended) this choice uses fewer words to convey the desired meaning. More effective writers never use insofar as in place of since. They use insofar as only as an alternative to to the extent that.
Because the usage is so precise, writers can easily test which word(s) will serve best. If exchanging to the extent that makes sense, then insofar as is appropriate. Otherwise, replace insofar as with since.
Consider the example sentence in the cropped graphic above. Replacing insofar as with to the extent that yields