Keep Your Syrup Warm is my best advise, and perhaps make the holes a bit larger.
If I have to feed syrup 'inside' my hives (due to them being light or the weather prevents flight) in the Fall or Spring I make absolutely certain its kept warm, changing it out each day.
Put simply; Bees won't take cold syrup.
However, at this time of year when daytime temps still can reach into the 40's (F) and bees are flying about seeking nonexistent forage I open feed (warm syrup). Its true that yellow jackets make up a portion of those consuming but its minimal and has proven unproblematic for my bees.
I do have the luxury of the available land to place open feed quite a distance away, well over 100 yards from the bee-yard.
The only time I've had a robbing issue occurred when I wasn't feeding at all so that has pretty much been a non-issue when open feeding.
Yep, 'all beekeeping is local.' Even making repeated comparisons to the climates of Finland and Alaska (or any other locals that are on opposite sides of the planet) is questionable at best and lacks any true representation of a similar 'assumed' climate.
Its more than that. IMO; it has much less to do w/ latitudes and longitudes than w/ the actual region bees are being kept. There are too many variables to generalize, whether its methods or opinions.
Although 'most' Beeks will do things different from other Beeks it is never reason enough to condemn or ridicule anothers methods, which only shows a lack of vision and/or tolerance from those doing the condemning or ridiculing.
But hey, some folks already know everything there is to know whether its beekeeping or life, so for entertainment sake lets let them continue to think so :-D