Are you asking a question about Rolemaster or Not RM? [The game you specified comes up as Not-RM do to a separation of ICE and Tolkien Enterprises] We also really need to know the rule set you are using RM2, RMC, RMSS, RMFRP, SM:P or SM2 as they might be different in every system. If you also can list the page # and a chart that would also help people answer your Q.
In general for RMSS I have the spear be -10 1H and +5 2H but that is just me. If the mods in the book say 1h -5OB and the 2H +10 OB then the OB mod for 2H would be +10 and not -5+10=+5.
Does that help?
MDC