IGF-1 levels are mostly hGH dose dependent and proportionate.
IGF-1 is produced in the liver in response to serum GH. The amount of IGF-1 generated varies from one individual to another. Liver health also matters and some steroid that lead to high AST/ALT labs may reduce IGF-1 response.
Time under the GH curve is more important that area under the curve. hGH IM injections will create higher serum GH peaks, but will deliver lower IGF-1 results than SC/SG injections. One can extend that to an expectation that more than one hGH injection per day would yield higher IGF-1 levels. The key points are that the half-life of GH in the blood stream is rather short, SC/SQ will create more sustained GH presence in the blood. High peak serum GH levels can be expected to run into linearity problems where more GH will not create a higher IGF-1 generation rate as the liver is maxed out and more GH does nothing more.
In my case, IGF-1 labs based on IM injections were a lot lower than SC/SQ injections at same dose of same Rx brand. I have charts over the years where my SC/SQ IGF-1 vs hCG dose is extremely linear and then one can characterize an individual person's IGF-1 response simply as the slope of the line as a single number.
In a GH replacement context, it take 6 weeks to really reap the benefits of hGH injections, but you have to keep in mind that that is relative to a long term state of having low GH and IGF-1 levels. Also in this context, direct GH labs have little or no value at all, but we still see doctors doing GH labs.