Live in-play middling?

[Sportsbook86]

Anyone able to help me on figuring out the expected value on this play?:

I bet the Texans/Raiders Over at 43, then at half time I placed a bet on Under 23 points in the 2nd half (game was currently at 28 total points making my bets O43 and U51.) I was wondering if I am losing value by trying to middle an already winning pick or if it is a good play.

[tomcowley]

Would you think U23 was a good bet if you suddenly realized you had left o43 hanging on the confirm screen? It's the same answer either way.