The Deans boss says his in-form squad will have their work cut-out coming up against 'very good' Purples side on Saturday.
Horndean head into the meeting on the back of three successive league victories and have scored 13 times, conceding just once in that period.
But Birmingham stressed his troops are going to have to be at their best if they are to extend their unbeaten Wessex League start to five matches when Stoneham visit Five Heads Park.
The Deans boss said: ‘We know Stoneham is going to be the toughest game of our season so far, without a doubt.
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‘Stoneham are a good side, they’re very honest and hard working, I think James Phillips the manager - for a young boy - I think he has done very well for his first managerial job there.
‘He’s got together a great squad who want to work and play for each other.
‘We’ve got a real, real tough game against AFC Stoneham, who have already come to the PO postcode and beat Moneyfields in the FA Cup.
‘We know they’re a very strong, physical side, everything goes through Cal Laycock up top, they’re a very honest side.
‘We’ve got to make sure we’re on our best to try to contain Cal Laycock, who is a good target man, we’ve got to try to nullify him and hopefully try to impose our game as well.’
Horndean's storming start to the season sees them currently sitting second in the table, just two points off leaders Brockenhurst with a game in hand.
However, Birmingham insisted no-one at the club will be getting carried away at such an early point in the campaign.
And he believes it could take even longer for clubs across the division to find a consistent level of performance given hampered pre-seasons because of the coronavirus pandemic.
Birmingham said: ‘Normally people say you get a rough jist of it after 10 games, it could be longer with everyone who’s had to get everything sorted for pre-season, which has been a difficult pre-season. It could be a good 15 games before there is a real consistency amongst everyone.
‘These games are now coming thick and fast, there are no easy games in the Wessex Prem.’