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

t = int(input())
for i in range(t):
    n = int(input())
    a = list(map(int,input().split()))
    if(len(set(a))==1):
        c = -1
    else:
        b = max(a)
        for j in range(len(a)-2,0,-1):
            if(a[j]==b and (a[j+1]<b or a[j-1]<b)):
                c = j+1
                break
        else:
            if(a.index(b)==0 and a[1]<b):
                c = 1
            else:
                c = len(a)
    print(c)
