All plants are great at sign language, it's just a matter of you learning it as well. You can either take action,or just let them do their own thing, depending on the signs that they give out.
Let's start with an easy example, leaf curl. This can be a sign of over watering. Tomato plants prefer a little and often when it comes to watering. However, we cannot always do this. If I am going out for the day and know it's going to be really hot, I sometimes give the soil a good soaking, it also adds humidity to the poly tunnel, which is good for tomatoes and helps fruit setting. I do not worry too much about this sign.
Another sign of over watering is a discolouration of the leaves, as it shows a lack of nutrients. Pale yellow patches are the first sign. I use a seep hose for most of my watering. But some plants need more water than others depending on how much fruit they have on them, or maybe in a warmer part of the poly tunnel, so it is a job to get even watering, which is another reason that I sometimes water with a can or a hose, as I can give the dry ones a little more.
If you are worried about it, then a little more feed for these plants will help. If you can give them a little less water, they will probably right themselves. However, if it is the majority of the crop, then you really need to up your feeding. As you can see, this plant is curling and has yellow patches, a classic case of too much water.
Thin heads are a sign that your plant is overloaded with fruit, so this will need action on your part. A few feeds of high nitrogen, which is normally used on flowers will help a lot. Normal tomato feed is high in potash, which is for fruit production, but as you can see, there is no lack of fruit.
The cause of this can be twofold, it could be a lack of nitrogen in the soil, or planting the plants in the soil too late. The planting time is quite crucial, too early and you will have too much foliar growth, but this is more a problem in grow bags with a higher concentration of fertilisers in the early stages. Too late and you have a lot of fruit set, which will slow down the foliar growth.
These plants are slightly more balanced and will not get their growth stunted by all the fruit. Both sets were planted at the same time, but one is a heavier fruiting variety. The overloaded ones above are Beefsteak. So it maybe best to get those in slightly earlier.
My upside down planter is looking better now that the head is getting more light. I will keep it in the poly tunnel as long as I can.
We can all get carried away trying to produce a good crop, but get the basics right and most plants will give you an excellent crop. It is commercial growers who are trying to produce as much fruit as possible per plant that always need to fine tune their plants, as they have invested a lot of money in heating and equipment to produce an early crop, when prices are higher. All I like to do is pass on a few tips as it is always handy to know what your plants are trying to tell you.