ontape -l roll-forward of many logs

IDS v7.31 UD8 on solaris I'm doing a logical log rollforward. The logs are backed up by an ontape -a process, to disk, and are about 10m each in size. It's all working fine if i roll forward one log then in a seprate screen move the next one into position. But this is a pain in the arse: I have hundreds to do and want to do them in one fell swoop. But if I cat all 100 into one large file ontape bombs out almost immediately asking if I have more logs. Similarly if I run onlog on the 1concatenation of 100 logs it reads just the first one and ask me if I have any more. Why is this happening? I've changed LTAPESIZE in the ONCONFIG file on the restored server from 10m to 2g but it's made no difference. SOMETHING is teling ontape/onlog to read only the first 10m of the concatenated file. But what?! Thx Neil