But the affable striker admits he’ll be judged on his goalscoring and not the cheer he brings to the Blues dressing room.
He’s scored two goals in six appearances to date, although the forward has featured from the outset only three times.
Boss Kenny Jackett has mainly preferred John Marquis as the lone frontman in Pompey’s 4-2-3-1 system.
Despite being confined to a support-act role so far, Harrison hasn’t been sulking around the training ground.
And nor does he plan to, with the Welshman pledging he’ll remain the bubbly character he is.
But Harrison accepts he also needs to weigh in with his own contributions on the pitch.
He said: ‘There is no need to bring other lads down when they're doing well. What’s the point in me coming in and sulking around the place?
‘It’s like rotten fruit in a basket. If you leave one piece of rotten fruit in there then it’s going to rot everything else.
‘That’s not me. If I did come in and start kicking up a fuss then that would be out of character for me and I don’t want that.
‘I’ve always been a bubbly character. Don't get me wrong, I’ll have my days like everyone, but I like to infect everyone with positivity rather than negativity.
‘Life’s too short to be down all the time, and in the past 18 months I’ve had enough downs to last a lifetime with the injuries I’ve had.
‘Touch wood, I’m okay now, train every single day and hopefully get more games but that’ll come as well.
‘If I could have had two or three more goals then I’d have been happy. If I'd have scored two goals in different games then maybe it’d be better.
'I want to go on a run of games and goals. That’s what strikers are judged on, not coming in and being happy every day – I’d be in the Premier League if that’s the case!
‘Strikers are judged on goals but it’s only going to get better. We’re going to have a good go at promotion this year.’
Jackett was a long-term admirer of Harrison, finally completing a deal at the third time of asking.
And the ex-Bristol Rovers man told how his personality was a factor in him being brought to Fratton Park.
He added: ‘I’ll never change around the place for anyone and the manager wanted me to come in bubbly when I spoke to him before I signed.
‘I know the gaffer here likes it and it works. I come in positive every day and will never spread and negativity around the place because it festers and we don’t need that.’