The call came after the DRS zone on the main straight at last weekend's Azerbaijan GP was cut by 100 metres, to the frustration of some drivers.
However, Alonso pointed out that the FIA knows from data gathered at last year's races that both tracks were among the easiest for overtaking under DRS, and he agrees with the move to trim the zones.
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And, while the Baku change generated some controversy, Alonso insisted that certain cars were hurt more than others, which is why their drivers voiced their frustration.
"I think so, yes," said the Aston Martin driver when asked if he backed the FIA decision to trim the Miami zones.
"It was the easiest here last year, apparently, so that's why I think FIA did shorten the DRS. In Baku it was one of the easiest last year, so they shortened the DRS.
"I heard Lewis [Hamilton] was saying that the DRS was too short, which I think for them with the high downforce it was too short. For Red Bull, it was too long.
"At the start/finish line, [Max Verstappen] overtook [Charles] Leclerc and he was opening to brake on the outside for Turn 1. So, if you are one car, it was too long. If you take another car, it was too short.
"So I guess it was about the calculation that the FIA do after seeing last year's races. Baku and Miami, they were on the high side in terms of overtaking, and how easy it was.
"So that's why they shortened it. Let's see this year, but it's difficult to predict."
Source: Autosport