House Size in a Chart
I generally use the Placidus House System, which is a Quadrant system, and as you have noticed unless the person is born on the equator, the houses will be different in size.
In extreme Northern or Southern latitudes some houses may span 60 degrees and others may be as small as 15 degrees or less.
All houses deal with a specific area of life.The ruler of the house is the planet that represents the sign on the cusp of the house (or intercepted sign(s)), the ruler of the house is not necessarily located in that specific house and tells a lot about how the individual interprets that area of life depending on the house it is located, the sign it is in, and aspects it makes to otherplanets in the chart.
In this case the house size doesn’t matter.Any planets located in a house gives a lense through which the activities of that house are viewed by the individual. Obviously if a house is large there is more chance of having a planet(s) residing within its boundaries. This will place an emphasis on the area for the individual. Any transiting planets will take longer to travel through some houses than others, making the experiences in the larger houses taking a longer time to learn and experience; and the thought is that transiting planets through the smaller houses do their job in a more concentrated way driving the lesson home faster and harder.
All the houses as a whole have to be looked at together rather than individually. The ruler of your 5th house of romance may be Mercury, and Natal Mercury may be in the 11th house conjunct your Sun etc. You find romance and have fun in large groups of friends, you are outgoing and like to communicate with people, this interaction with large groups of the general public brings romantic partners into your sphere to meet etc. The size of your 5th house has nothing to do with any of this. If there are planets in the fifth, this is the type of person and experience you are looking for(the lense you use for judgment) in romance, these are the types of experiences you enjoy. etc.