Multi Cast Paging 4+ handsets

I have a W60 base with 7 56H handsets. I cannot get all 7 handsets to receive the page at the same time. When a multicast page is received, only 4 handsets receive the page. If I page a second time, the other 3 receive the page but not the first 4.

I have the active handsets set to 8 on all accounts and the registered handset set to 8 as well.

Is this a limitation?