70+75 meters Straight, 65 meters square boundaries are not small per se but modern batters can clear it quite easily. Dead pitches also help it as batters can time the ball ridiculously well. The problem comes when you deliberately shorten the boundaries to 60 meters (straight), luckily it stopped in the IPL and you hardly see 60-meter boundaries, unless you are using side pitches (one side boundary becomes way too small like it's a woman's cricket).
You can't solve this short boundaries problem in existing grounds because stadiums are small but there should be enough space in new grounds for 80-90 or even 100-meter boundaries (Straight).
While teams are playing in New Zealand and South Africa we have never talked about short boundaries but here usually things gone in this way I am not well aware about what are the rules about this, but we need to be had 70 meters minimum boundaries for men cricket because it is important and surely can do good for them having small boundaries are surely never been ideal situation and on existing grounds doing this is more problematic for the boards.
But, we still need some good specific rule from ICC about this because I watch few matches recently in different countries, and we have many small boundaries even in few we have nearly 55 meters which are surely not good for the men cricket specially while you are playing on dead pitches and bowlers are surely praying for hell instead of playing on pitches and conditions like these.
New Zealand is a special case, they have small grounds so they can't do much about it and it's a fact that not every stadium can accommodate 75-meter boundaries.
Usually, it's a minimum 60-meter mark from the center of the pitch but old stadiums are not made to accommodate the same boundary size from every direction, here comes the short Square boundary problem, sometimes it's like 55-ish meters which is a big joke. However, In the last WC ICC gave a recommendation of a minimum of 70 meters boundaries for every venue and it was followed accordingly.
