MCT will only matter if you are on one ticket and EI won't sell you a ticket at below MCT. If EI is late into BOS and that causes a misconnect, it willl be for EI to rebook you and as you will be on a flight departing the EU, take care of your hotel & food as well as pay delay compensation if all of that kicks in.

If you are on two tickets, MCT is irrelevant and your B6 ticket will be cancelled if you no show. At that point, you will be at B6's mercy as to whether you are rebooked or must purchase a new ticket.

For this reason, I generally allow 2-3 times the transfer time across tickets than for connections. You are stuck with the risk of inbound delays and the like and EI's obligation ends at the termination point of its ticket, e.g. BOS. You would only be due compensation at 3 hours or 4 hours (EUR 300 vs EUR 600).