Perhaps I'm misreading things here (apologies if so) .... but have to say I'm a tad confused.

On the one hand, the OP talks about his "large suitcase" having gone astray in the past, so presumably this is the same case that he is now looking to carry with him onboard and thus avoid any recurrence.

He also says that the measurements comply with EK guidelines. But would any bag meeting such hand-baggage guidelines be realistically described as "a large suitcase" ....