1
3
5 3 4
 6
5
5 3 4 4 5
3
1 1 1
5
4 4 3 4 4
5
5 5 4 3 2
3
1 1 2
5
5 4 3 5 5
 1
3
10 1 5

1
 1
-1
2
2
3
1
 1

for _ in range(int(input())):
    n=int(input())
    list1=list(map(int,input().split()))
    p=max(list1)
    if len(set(list1))==1:
        print(-1)
        continue
    for i in range(0,len(list1)):
        if list1[i]==p and i+1<n and list1[i+1]!=p:
            print(i+1)
            break
        elif list1[i] ==p and i-1>=0 and list1[i-1] !=p :
            print(i+1)
            break