Figures released in parliament by children's minister Nadhim Zahawi show that in the first 11 months of the Adoption Support Fund (ASF), which opened to applications in May 2015, the average payout was £4,927.
For 2016/17, this figure fell to £3,638 and in 2017/18 was £2,920 - representing a 40.7 per cent drop in the space of two years.
However, the figures also reveal that the number of approved applications has risen significantly over the same period.
In 2015/16 there were 3,610 successful applications, rising to 7,191 in 2016/17 and 9,465 in 2017/18. That represents a 262 per cent increase.
In total £17.79m was paid out from the fund in 2015/16, £26.26m in 2016/17, and £27.64m in 2017/18.
A cap limiting how much could be claimed at £5,000 per child - known as the fair access limit - was introduced in October 2015 due to unexpected levels of demand.
Figures obtained by CYP Now earlier this year showed that over a 15-month period up to 5 January 2018, a total of 74 councils had contributed £686,711 to the cost of post-adoption support through "match funding" arrangements.
Under fund rules, when an adoptive family - or those caring for a child under a special guardianship order - is assessed as needing support or assessment costing more than £5,000 or £2,500 respectively, the amount over the caps should be matched by their council.
A DfE-commissioned evaluation study published last year found that although the ASF has resulted in improved outcomes for families, there have been a number of issues.
The report said the lack of capacity in the system is yet to be addressed due to a lack of confidence in the long-term future of the initiative.